The field of the disclosure relates generally to a controller for an electric motor and, more specifically, a controller that enables an increased torque output of an electric motor.
At least some known motor controllers are programmed to operate under a defined speed-torque relationship between the motor and a fluid mover (e.g., a blower, pump, or compressor). The motor controller controls delivery of current to the motor that defines a torque output of the motor, wherein the torque output is generally proportional to the current input. Different torque output profiles are available, to provide different levels of fluid flow under different settings (e.g., for air flow, heating, cooling, or fan settings). Generally, a higher torque output corresponds to an increased fluid flow. In some cases, the motor controller controls the motor to operate under constant-torque conditions, such that the motor is generally known as a “constant-torque motor.” In these cases, the torque output is controlled according to a speed-torque profile, under which torque is increased in a stepwise manner independent of speed. Specifically, the motor controller is configured to calibrate the motor using a plurality of calibration points (i.e., speed-torque measurements) to map the speed-torque relationship.
In other cases, the motor controller controls the motor to operate under constant fluid flow conditions, such that the motor is generally known as a “constant fluid flow motor.” In these cases, the torque output is controlled according to a speed-torque-fluid flow profile, such that adjusting a torque output of the motor facilitates control of the fluid flow output from the fluid mover in a predictable manner. Specifically, the motor controller is configured to calibrate the motor using a plurality of calibration points (i.e., speed-torque-fluid flow measurements) to map the speed-torque-fluid flow relationship.
For both constant-torque and constant fluid flow motors, a given profile is available from one tap of a plurality of taps. Put another way, each tap provides an output according to a particular pre-programmed profile (i.e., speed-torque profile, or speed-torque-fluid flow profile). For example, one tap corresponds to a “low-torque” motor setting, another tap corresponds to a “medium-low torque” motor setting, a third tap corresponds to a “medium-torque” motor setting, etc. A higher-torque tap may be selected (e.g., by an installer) for an increased fluid flow. For example, in a heating, ventilation, and air conditioning (HVAC) system incorporating such a motor to drive a blower, different airflow may be selected for different situations, such as cooling, heating, or circulating air. However, the fluid flow output from a given motor operating under a given torque output profile can vary according to the construction of the fluid mover, ductwork or piping through which the fluid flows, or other flow restriction. When the fluid flow restriction, or static pressure, is particularly high, higher torque output profiles may be selected to compensate therefor. Operating with a higher torque output profile requires more power, which can negatively impact an efficiency rating of the electric motor, even if the relative inefficiency is a result of compensation for environmental factors.